In a large bowl, combine remaining melted butter and cocoa powder. Using an electric mixer set on medium speed, beat sugar, eggs and vanilla into the cocoa mixture until well combined. Stir flour and salt into cocoa mixture until thoroughly combined. Spread mixture into prepared pan.

Bake brownies until a toothpick inserted in center comes out almost clean, 35-40 minutes. Transfer the pan to a wire rack to cool completely.

Lift uncut bars from pan using foil and place on a flat work surface. Using the tree-shaped cookie cutter, cut out tree shapes, inverting the cutter every other time to minimize waste.

Place melted chocolate into a reseable plastic bag; snip off 1 corner. Pipe melted chocolate in a zigzag design on top of trees; top with christmas sprinkles.